When Buying an Opal
Many factors must be considered when valuing
opal. Black or dark opal is in general more valuable than light opal. The intensity
or brilliance of colour is of most importance. The finest of opals are
maximum brightness and clarity. There should be an even play of colour all
over the stone with no patches of colourless opal. For the highest value,
all colours should be present, especially red which is the rarest. Marks on
the base usually have no effect on price. The stones should be free from
obvious flaws on the face of the opal.
To inspect rough opal you need a good
light source. Sunlight is good to detect colour that may be hidden under a
surface coating, and is excellent for the basic sorting of material.
However a desk lamp with a higher wattage incandescent bulb is good to help
determine facing direction, and to hold stones up to the rim so as to look
through, and pick up inclusions.
Individual opals respond differently to different light sources - for
example many lighter types of opal will fade under fluorescent light,
whereas black opal will still show colour.
Each Nobby has an opaque skin
which hides the colour within - often this could be a layer of grey potch,
which will need to be snipped off using tile snips, or sawn or ground off
(use the latter tools where expensive opal is involved).